# Multiple queue mode
<a name="queue-mode"></a>

AWS ParallelCluster version 2.9.0 introduced multiple queue mode. Multiple queue mode is supported when [`scheduler`](cluster-definition.md#scheduler) is set to `slurm` and the [`queue_settings`](cluster-definition.md#queue-settings) setting is defined. This mode allows different instance types to coexist in the compute nodes. The compute resources that contain the different instance types can scale up or down as needed. In queue mode, up to five (5) queues are supported, and each [`[queue]` section](queue-section.md) can refer to up to three (3) [`[compute_resource]` sections](compute-resource-section.md). Each of these [`[queue]` sections](queue-section.md) is a partition in Slurm Workload Manager. For more information, see [Slurm guide for multiple queue mode](multiple-queue-mode-slurm-user-guide.md) and [Multiple queue mode tutorial](tutorial-mqm.md).

Each [`[compute_resource]` section](compute-resource-section.md) in a queue must have a different instance type, and each of these `[compute_resource]` is further divided into static and dynamic nodes. Static nodes for each `[compute_resource]` are numbered from 1 to the value of [`min_count`](compute-resource-section.md#compute-resource-min-count). Dynamic nodes for each `[compute_resource]` are numbered from one (1) to ([`max_count`](compute-resource-section.md#compute-resource-max-count) - `min_count`). For example, if `min_count` is 2 and `max_count` is 10, the dynamic nodes for that `[compute_resource]` are numbered from one (1) to eight (8). At any time, there can be between zero (0) and the max number of dynamic nodes in a `[compute_resource]`.

The instances that are launched into the compute fleet are dynamically assigned. To help manage this, hostnames are generated for each node. The format of the hostname is as follows:

`$HOSTNAME=$QUEUE-$STATDYN-$INSTANCE_TYPE-$NODENUM`
+ `$QUEUE` is the name of the queue. For example, if the section starts `[queue queue-name]` then "`$QUEUE`" is "*queue-name*".
+ `$STATDYN` is `st` for static nodes or `dy` for dynamic nodes.
+ `$INSTANCE_TYPE` is the instance type for the `[compute_resource]`, from the [`instance_type`](compute-resource-section.md#compute-resource-instance-type) setting.
+ `$NODENUM` is the number of the node. `$NODENUM` is between one (1) and the value of [`min_count`](compute-resource-section.md#compute-resource-min-count) for static nodes and between one (1) and ([`max_count`](compute-resource-section.md#compute-resource-max-count) - `min_count`) for dynamic nodes.

Both hostnames and fully-qualified domain names (FQDN) are created using Amazon Route 53 hosted zones. The FQDN is `$HOSTNAME.$CLUSTERNAME.pcluster`, where `$CLUSTERNAME` is the name of the [`[cluster]` section](cluster-definition.md) used for the cluster.

To convert your configuration to a queue mode, use the [`pcluster-config convert`](pcluster-config.md#pcluster-config-convert) command. It writes an updated configuration with a single [`[queue]` section](queue-section.md) named `[queue compute]`. That queue contains a single [`[compute_resource]` section](compute-resource-section.md) that is named `[compute_resource default]`. The `[queue compute]` and `[compute_resource default]` has settings migrated from the specified [`[cluster]` section](cluster-definition.md).